The present invention relates to the compensation of a change in timing information caused by thermal variations, and in particular relates to differential amplifiers.
Most electronic circuits appear to be sensitive on thermal variations caused mainly by variations in ambient temperature or by dynamic behavior due to power consumption. In particular, different thermal variations at different locations of electronic circuits often lead to an unwanted behavior of the circuit.
In digital systems, information is mainly transmitted or processed by means of signals changing from one state to another. Timing information comprises the information about when a signal is due to change. A digital circuit, which is processing or transmitting timing information, generates a sequence of output state transitions as a result of a sequence of input state transitions. The relationship between timing information of input transitions must be reflected at the output of the system. Furthermore, the time elapsing between input state changes should also elapse between output state changes caused by their respective input state changes. Otherwise, the system has changed the timing information, which should be avoided in most applications.
UK-A-2316559 discloses a temperature compensated driver circuit that is relatively stabilized in waveform amplitude and output timing by detecting the power consumption of its output driver stage and correcting and controlling the power consumption. A temperature detector detects the temperature changes of output elements and a temperature compensator adjusts the timing of an output signal against an input signal in response to a temperature-detecting signal from the temperature detector. This, in particular, allows compensating timing deviations due to a temperature-induced variation of a pulse delay time.
In digital circuits, it has been observed that thermal variations can lead to a timing drift dependent on the duty cycle as the ratio of the sum of all pulse durations to the total period. Most conventional circuits are therefore designed to provide a good thermal coupling between corresponding components which has been shown to reduce this so-called duty cycle drift, i.e. the variation of the propagation delay dependent on the duty cycle, from e.g. 2 ns to 0.5 ns. In modern digital applications, however, thermal coupling has proved not to be sufficient to reduce the duty cycle drift e.g . down to values of 100 ps or smaller. Furthermore, for physical reasons it is clear that an ideal thermal coupling will never be possible, so that thermal coupling, even if significantly improved, will always have a natural limitation.
As apparent from the above said, it is clear that a timing information, such as the duty cycle drift or variations in the delay time as explained in GB-A-2316559, can be changed by thermal variations.